1. Field of the Invention
The present invention relates to a full-color toner kit, a process cartridge, and an image forming method for use in electrophotography.
2. Discussion of the Background
New models of consumer oriented laser printers are often expected to be smaller in size, lower in cost, and higher in printing speed than previous models.
To make a printer smaller in size, a fixing device can be made to include two rollers without an oil applicator. As an alternative to applying oil to a fixing roller, a toner for use in such a fixing device may include a release agent (e.g., a wax) so that the fixed toner image can easily separate from the fixing roller. If the toner includes too much wax, the toner may have too large a cohesion force. As a result, the toner may excessively stick to a control blade that charges the toner, and therefore the resultant image can have white line defects. (This phenomenon is hereinafter referred to as the “toner-sticking problem”.)
As colorants for use in toners, naphthol, benzimidazolone, and copper phthalocyanine can be used as magenta, yellow, and cyan colorants, respectively. As resins for use in toners, a combination of a resin containing a wax capable of improving dispersibility of the wax in the resultant toner and a resin having a lower softening point capable of increasing translucency, color reproducibility, and glossiness of the resultant image is typically used.
When yellow, magenta, and cyan toners each include the same amount of resin containing a wax and resin having a low softening point so that each toner includes the same amount of the wax, the magenta toner has a higher softening point compared to the other toners. Therefore, the magenta toner tends to cause an offset problem in that a part of a fused toner image is adhered and transferred to the surface of a heat member and then the part of the toner image is re-transferred to an undesired portion of the sheet itself or the following sheet of a recording material at low temperatures.
Japanese Patent No. 3584141 describes a toner including three kinds of resins to improve thermal properties of the toner. However, no attempt is made in this reference to adjust the mixing ratio of the resins according to the kind of colorant used.
Published unexamined Japanese Patent Application No. 2004-70005 describes a red toner including a polyester resin and a naphthol colorant. It is described therein that the toner overcomes disadvantages of a combination of a polyester resin and a naphthol colorant. However, the red toner is not necessary to produce full-color images, and does not solve the problem of the magenta toner.